Chemical Oxygen Demand (COD) from Bioscience is a test method for determining the level of total oxidizable organic matter in a water sample. Chromic acid contains chromium ion in a +6 valence state. This ion has an orange color and is a strong oxidizing agent. When chromium +6 reacts with an oxidizable compound it is reduced to chromium +3, a blue-green ion, and the pH increases proportionately with the oxidation. Various compounds are added to eliminate the effects of interfering reactions. The results are quantified using the colorimetric method (measuring the change in color) or titrimetric method (measuring the increase in pH). The accu-TEST COD Reagents contain a precisely measured reagent in spectrophotometric glass vials. They are heated at 302 degrees F for two hours in the accu-TEST Reactor, which creates an internal reflux within the sealed vials. The vials are cooled and read on a colorimeter or titrated to obtain the final results. 800/627-3069; www.bioscienceinc.com.